1-Chloroethyl chloroformate [CAS 50893-53-3] and 2-chloroethyl chloroformate [CAS 627-11-2] are known compounds which are useful as intermediates for the synthesis of pharmaceuticals and herbicides. Although these compounds can be produced by the chlorination of ethyl chloroformate [CAS 541-41-3] in the liquid phase or in the vapor phase, the reaction products are heavily contaminated with one or more dichloroethyl chloroformates as by-products. The formation of higher chlorinated by-products is undesirable since the by-products are of lesser value economically and since they often result in disposal problems.